1. Field of the Invention
The present invention relates to a system for collecting carbon dioxide in flue gas, capable of stably processing all the carbon dioxide in the flue gas discharged from an industrial facility such as a gas turbine, a furnace, or a boiler.
2. Description of the Related Art
Conventionally, to collect carbon dioxide in flue gas, for example, a system is adopted when an amine-based absorbing solvent is used as a CO2 absorbing solvent to remove and collect CO2 from flue gas; firstly, a process is performed to bring the CO2 absorbing solvent into contact with the flue gas in an absorption column, and thereafter the CO2 absorbing solvent that has absorbed CO2 is heated in a regeneration column; secondly, CO2 is freed and the CO2 absorbing solvent is regenerated, and circulated in the absorption column again, and finally, reused (for example, see Japanese Patent Application Laid-open No. H3-193116).
FIG. 9 is an example of a conventional system for collecting CO2 in flue gas. As shown in FIG. 9, a conventional CO2 collecting system 1000 includes an flue gas cooling device 1004 that cools flue gas 1002 containing CO2 discharged from an industrial facility 1001 such as a boiler and a gas turbine by cooling water 1003, a CO2 absorption column 1006 that brings the flue gas 1002 containing cooled CO2 into contact with a CO2 absorbing solvent 1005 absorbing CO2 to remove the CO2 from the flue gas 1002, and a regeneration column 1008 that releases the CO2 from a CO2 absorbing solvent (rich solvent) 1007 absorbing the CO2 to regenerate the CO2 absorbing solvent. In this device, a regenerated CO2 absorbing solvent (lean solvent) 1009 from which the CO2 is removed in the regeneration column 1008 is recycled as the CO2 absorbing solvent in the CO2 absorption column 1006. The CO2 absorption column 1006 and the regeneration column 1008 configure a CO2 collecting device 1030.
In a CO2 collection method using the conventional CO2 collecting device 1030, the flue gas 1002 containing CO2, discharged from the industrial facility such as a boiler and a gas turbine, is firstly sent to the flue gas cooling device 1004 after pressure is raised by an flue gas fan 1010, cooled by cooling water 1003, and thereafter sent to the CO2 absorption column 1006.
In the CO2 absorption column 1006, the flue gas 1002 is countercurrently contacted with, for example, the CO2 absorbing solvent 1005 based on an amine-based absorbent, and the CO2 in the flue gas 1002 is absorbed in the CO2 absorbing solvent 1005 due to a chemical reaction (R—NH2+H2O+CO2→R—NH3HCO3), and flue gas 1011 from which the CO2 is removed is released from the system. The CO2 absorbing solvent 1007 absorbing the CO2 is also called a rich solvent. Pressure is raised for the rich solvent 1007 by a rich solvent pump 1012, and heated by a rich/lean solvent heat exchanger 1013 by the CO2 absorbing solvent (lean solvent) 1009 regenerated by removing CO2 in the regeneration column 1008 described later, and supplied to the regeneration column 1008.
The rich solvent 1007 released from the upper part of the regeneration column 1008 to the interior of the regeneration column 1008 receives heat from water vapor generated inside the regeneration column 1008 and a large amount of CO2 is discharged. The CO2 absorbing solvent from which a portion or a large amount of CO2 is released inside the regeneration column 1008 is called a semi-lean solvent. The semi-lean solvent becomes a CO2 absorbing solvent from which almost all of the CO2 is removed by the time it reaches the lower portion of the regeneration column 1008. The absorbing solvent regenerated by removing almost all of the CO2 is called a lean solvent. A re-boiler 1014 heats the lean solvent by using steam. Meanwhile, CO2 gas 1015 together with water vapor released from the rich solvent and the semi-lean solvent inside the regeneration column 1008 is derived from the head top part of the regeneration column 1008, the water vapor is condensed by an overhead condenser 1016, water is separated by a separation drum 1017, and CO2 gas 1018 is released from the system and collected. The water separated by the separation drum 1017 is supplied by a condensed-water circulating pump 1019 to the upper part of regeneration column 1008. The regenerated CO2 absorbing solvent (lean solvent) 1009 is cooled by the rich solvent 1007 by the rich/lean solvent heat exchanger 1013, which is followed by raising the pressure by a lean solvent pump 1020, and the resultant water is cooled by a lean solvent cooler 1021, and thereafter supplied to the CO2 absorption column 1006.
In FIG. 9, reference numeral 1001a is a stack flue of the industrial facility 1001 such as a boiler and a gas turbine, and 1001b is a stack having a damper on the inside. There are cases that the CO2 collecting device is installed after the system is completed to collect CO2 from an existing source of the flue gas and cases that it is simultaneously attached to a new source of the flue gas.
As the conventional effective utilization of the carbon dioxide in flue gas, some of the carbon dioxide in flue gas is merely collected to produce carbon dioxide for carbonated drinks and dry ice. However, the greenhouse effect caused by carbon dioxide is recently pointed out as one of the causes of global warming. Measures are becoming an urgent necessity internationally to protect the global environment, and also, the source of generating the carbon dioxide affects every field of human activity, which burns fossil fuels, and demands of restricting the discharge tend are becoming even stronger. Along with this tendency, in power generation facilities such as thermal power stations that use a large amount of fossil fuels, there have been a method in which flue gas of industrial facilities such as a boiler and a gas turbine is brought into contact with a CO2 absorbing solvent, all of CO2 in the flue gas is removed and collected, and a method for storing the collected CO2 without releasing it into the atmosphere.
As described above, in the conventional CO2 collecting system 1000, there has been proposed that, when collecting all of carbon dioxide in flue gas, a containing unit such as a valve or damper that can be opened and closed inside the stack 1001b, as shown in FIG. 9, is installed to close and stop during the operation of the CO2 collecting device and to release when the operation of the CO2 collecting device is stopped while the source of the flue gas is kept operating.
However, at the time of stopping the operation of the CO2 collecting device, unless an operation such as containment of the valve, damper or the like, which closes the interior of the stack or releasing is surely performed, discharge of flue gas is not performed smoothly, and there are occasions that the industrial facilities (such as gas turbines) at the upstream side are adversely affected.
Further, in a turbine facility that generates electricity of 200,000 kilowatts in which 3000 ton of carbon dioxide are processed in each day, an amount of discharged flue gas becomes enormous and a stack having, for example, a diameter of 7 to 10 meters is required. Under such circumstances, a facility of a containing unit such as a valve and a damper that contains the flue gas needs to be larger.
Accordingly, a system capable of drawing in substantially all of a large amount of flue gas to a carbon-dioxide collecting device in a simple, stable, and safe manner has been desired.